Products made of cellulose fiber such as paper, paper board and woody fiberboard hitherto have been generally produced by adding a sizing agent to an aqueous dispersion of cellulose fiber. As the sizing agent, rosin sizing agents which are chemicals for paper making which can impart water resistance, ink resistance, penetration resistance and the like to obtained products have been usually widely used. The effect of the sizing agent can be for the first time exhibited by fixing the sizing agent on fibers together with aluminium sulfate. Therefore, evil influence due to the use of the aluminium sulfate has been pointed out. That is, since paper is compulsively produced under an acidic condition, there are some problems such as deterioration of properties of produced paper with the passage of time, troublesome treatment for wastewater and corrosion of paper machines. When calcium carbonate which is a cheap filler is used, there is a disadvantage that calcium carbonate decomposes to generate carbon dioxide gas since paper is produced under an acidic condition. Therefore, the filler could not be used.
As a means to solve the above problems, a paper making method under a neutral condition in which aluminium sulfate is not substantially used, has been developed, and ketene dimer sizing agents have been wellknown as one of neutral sizing agents used in the method.
Since the ketene dimer sizing agent is generally stored in a state of aqueous dispersion and used, it is necessitated that the ketene dimer sizing agent is good in stability. However, conventional ketene dimer sizing agents have a mortal defect that the sizing agents are inferior in storage stability due to crystalline property of the ketene dimer component which is a dispersed phase thereof. Also, a method for adding various kinds of noncrystal components has been proposed to improve the stability. However, the method has a defect that the sizing effect is lowered.
The present inventors have eagerly studied to solve the above-mentioned problems with aiming at a material which can act as an agent for improving the stability. As a result, they have found a marvelous fact that a specific polymeric aluminum compound can remarkably improve the storage stability of aqueous dispersion of ketene dimer sizing agent and does not deteriorate the original sizing property of ketene dimer. The present invention has been for the first time accomplished on the basis of the facts.